Processes and methods for binary opposing buoyancy for large underwater lift applications

ABSTRACT

A deep-sea apparatus for retrieving deep-sea nodules is provided. The deep-sea apparatus includes an opposer configured to provide static buoyancy to the deep-sea apparatus. The deep-sea apparatus further includes a thruster coupled to the opposer, the thruster configured to provide dynamic buoyancy to the deep-sea apparatus. The deep-sea apparatus also includes a variable load and a gas supply system that includes a gas cylinder connected to a gas valve of the opposer, where the gas supply system is configured to inject a predetermined amount of gas from the gas cylinder to the opposer in response to a change in a vertical position of the opposer caused by a mass change in the variable load.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication No. 63/394,199, titled “PROCESSES AND METHODS FOR BINARYOPPOSING BUOYANCY FOR LARGE UNDERWATER LIFT APPLICATIONS,” which wasfiled on Aug. 1, 2022 and is incorporated herein by reference in itsentirety.

FIELD OF TECHNOLOGY

The present disclosure relates generally to deep-sea mining systems andmore specifically to a dynamic buoyancy system for a deep-sea miningsystem. The dynamic buoyancy system applies variable buoyancy conditionsthat allow the deep-sea mining system to descend, collect ore nodulesfrom the seabed, and ascend without seabed contact to limit theenvironmental impact.

BACKGROUND

As the world transitions to green energy solutions, there is a growingdemand to store energy in reusable batteries made from critical metalssuch as nickel, copper, and cobalt. Currently, there are fewer sourcesof these metals remaining on land and these land-based resources can bein challenging places and/or within sensitive ecosystems. Deep seamining is an un-tapped source of critical metals in the form of orenodules (e.g., polymetallic ferromanganese nodules) and has been thefocus of the mining industry in recent years.

Technical difficulties associated with deep-sea mining include the oceandepths (e.g., 5 km to 6 km) and the extreme pressures (e.g., between 500bar and 600 bar) at which the mining of the ore nodules occurs, and thetechniques required to transport the mined ore up to the ocean surface.There are two systems that have been widely examined and determinedfeasible on a small scale: (i) seabed dredging collector systems thatpump the ore to the surface as a slurry through vertical riser pipes,and (ii) mechanical lifting systems that use synthetic ropes. However,both systems suffer from reliability and scaling issues, and can causeirreparable damage to sensitive environments due to the disturbancescaused on the seabed during the mining process.

Therefore, there is a need for more sustainable ways to harvest mineralsfrom the sea floor whilst keeping the seabed ecosystem intact.

SUMMARY

A dynamic buoyancy system implemented for deep-sea mining systems andmethods for using the same are disclosed herein. According to someembodiments, the disclosed dynamic buoyancy system enables the deep-seamining system to hover at a predetermined distance from the seabedduring the entire mining process, which minimizes the environmentalimpact of the mining process. Further, the deep-sea mining system usingthe dynamic buoyancy system disclosed herein can be scaled and deployedas a fleet of vehicles with redundancy. According to some embodiments,the dynamic buoyancy system enables the deep-sea mining system todescend to the seabed, travel along the seabed without contact whilecollecting the ore nodules, and ascend to the surface to deliver itspayload. The dynamic buoyancy system applies variable buoyancytechniques and employs opposer/thrust devices designed to work in apower-reduced mode at the planned ocean depths as the deep-sea miningsystem descends, collects ore, and ascends without seabed contact andwith minimum environmental impact.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying figures, which are included as part of the presentspecification, illustrate the presently preferred embodiments andtogether with the general description given above and the detaileddescription of the preferred embodiments given below serve to explainand teach the principles described herein.

FIG. 1 illustrates an exemplary deep-sea mining system, in accordancewith some embodiments.

FIG. 2 illustrates an exemplary opposer/thrust device for deep-seaoperations, in accordance with some embodiments.

FIG. 3 is a top view of an exemplary buoyancy system featuring fouropposer/thrust devices for deep-sea operations, in accordance with someembodiments.

DETAILED DESCRIPTION

In deep-sea mining, as weight is added or removed from an underwatervehicle, buoyancy acting on the vehicle changes. It is thereforenecessary to compensate for the buoyancy changes attributed to weightloss or weight gain. The use of air bladders that expand and displacewater is an approach for adjusting buoyancy underwater. Because waterbecomes more dense with increasing pressure (e.g., at the depths wherepolymetallic nodules can be found and collected), more air is requiredto achieve the same amount of lift.

FIG. 1 illustrates an exemplary deep-sea mining system 100 deployed froma mining ship 110 to collect ore nodules 120 disposed on the seabed,according to some embodiments. Deep-sea mining system 100 descends atthe vicinity of the seabed and hovers over the seabed during the orecollection process. In some embodiments, deep-sea mining system 100includes an underwater autonomous vehicle (UAV) 130, an ore collectorsystem 140 that collects ore nodules 120 form the seabed, a payloadhopper 150 for temporarily storing the collected ores, and a dynamicbuoyancy system 160 that enables the deep-sea mining system 100 tomaneuver primarily in a vertical direction z (e.g., to descend from thesea surface to the seabed and ascend from the seabed to the seasurface).

According to some embodiments, UAV 130 is equipped with thrusters (notshown in FIG. 1 ) that enable deep-sea mining system 100 to maneuverprimarily in a lateral direction (e.g., parallel to the seabed-along thex-y plane) and secondarily in the vertical direction (e.g., along thez-direction). By way of example and not limitation, ore collector system140 can be equipped with robotic arms 140 a that may extend towards theseabed and reach for the ore nodules. In some embodiments, the roboticarms 140 a can harvest the ore nodules by picking them up as thedeep-sea mining system 100 hovers over the seabed using suitable endeffectors not shown in FIG. 1 . Once picked up, the ore nodules can bedisposed into payload hopper 150.

According to some embodiments, deep-sea mining system 100 usesunderwater surveying and inspection systems to locate the ore nodules120 on the seabed and to determine whether marine life is anchored onthe nodules. By way of example and not limitation, deep-sea miningsystem 100 may be configured to avoid collecting ore nodules havingmarine life anchored on them. Once the payload hoper 150 is full, thedynamic buoyancy system 160 enables the deep-sea mining system 100 toascend to the sea surface and deliver its payload. In some embodiments,the dynamic buoyancy system 160 is configured to keep the deep-seamining system 100 neutrally buoyant at any depth, and in particularclose to the operating depth, while limiting the use of electricallypowered thrusters to conserve energy.

According to some embodiments, the components of deep-sea mining system100 (e.g., dynamic buoyancy system 160, payload hopper 150, orecollector system 140, and UAV 130) operate in synergy. In someembodiments, these components may be either integrated in a singlehousing or operated as detachable modules physically and communicativelyconnected to one another. According to some embodiments, dynamicbuoyancy system 160, payload hopper 150, ore collector system 140, andUAV 130 are physically attached to one another during thecollection/mining process, and at least the payload hopper 150 and thedynamic buoyancy system 160 can be physically attached to one anotherduring the mining and ascending process. In some embodiments, thedynamic buoyancy system 160 can provide the necessary buoyancy tocompensate for the collected ores during the mining process and theascent of at least the payload hopper 150 or of the entire deep-seamining system 100. In some embodiments, if the dynamic buoyancy system160 and the payload hopper 150 ascend on their own to the ocean surface,UAV 130 may provide with its thrusters the necessary buoyancy todeep-sea mining system 100 until the dynamic buoyancy system 160 and thepayload hopper 150 descend again from the sea surface to re-attach tothe deep-sea mining system 100.

In some embodiments, deep-sea mining system 100 can include additionalcomponents, modules, and systems necessary for its indented operation.These additional components, modules, and systems are not shown in FIG.1 for simplicity. By way of example and not limitation, these additionalcomponents, modules, and systems may include cables, one or more onboardcomputers, electronic equipment, additional thrusters, motors,batteries, communication equipment, cameras, radars, controllers, globalpositioning systems, and the like. These additional components, modules,and systems are within the scope of this disclosure. In someembodiments, deep-sea mining system 100 may operate under autonomousmode, semi-automatic mode, manual mode, or combinations thereof based oninstructions from mining ship 110. In yet another embodiment, deep-seamining system 100 may be communicatively coupled and physicallyconnected to mining ship 110 via cables or other suitable means.

Autonomous or untethered submersible vehicles, such as the deep-seamining system 100, operate on a finite amounts of power. More often thannot, submersible vehicles use electric energy for producingpropulsion/thrust. When the lift or buoyancy adjustments for asubmersible vehicle are thrust based, there can be a substantialincrease in power and propulsion demand, which translates to acontinuous power usage of the vehicle's energy resources.

On the other hand, increasing the power storage of a submersiblevehicle, increases the vehicle's mass and volume, which is notdesirable. In aircraft design, lift, thrust for lift/speed, and weightare parameters carefully considered. For example, for a new aircraftdesign, when the mass of the aircraft increases, the lift acting on thewings of the new aircraft has to increase to offset the added mass. Liftincreases by increasing: (i) the wing surface area, which adds moreweight; and (ii) the provided thrust, which requires larger and heavierengines. A larger wing span also means a higher fuel capacity, whichalso adds weight. Therefore, there is a sequence of reciprocal cause andeffect in which two or more elements intensify and aggravate each other.The system described herein interrupts this reciprocal cause and effectcycle.

As the mass to be lifted increases and the time of non-static operationincreases, the weight of the vehicle and the power requirementsincrease. For example, the energy transferred to an object (e.g., thework done W) via the application of force F along a displacement S isprovided by equation (1) below:

W(Joules)=F(Newtons)·S(meters)  (1).

The work W performed during a period with duration t is provided byequations (2) below.

W(Joules)=P(Watts)·t(seconds)  (2),

where P is the power or amount of energy transferred per unit time.

Time domain complications exist when buoyancy sources interact withlarge changes in mass. As a result, related rates can cause the controlalgorithms governing these interactions to be non-trivial. In addition,submersible vehicles are mostly concerned with observation orinteraction tasks. Therefore, autonomous submersible vehicles taskedwith very large-scale collection of mass are rare. Autonomy and relativecollection of mass as a ratio to raw vehicle mass is even rarer.Accordingly, there are no known or established methods of energyreduction in prior systems. Advantageously, the deep-sea mining system100 disclosed herein is equipped with an opposer/thrust device thatminimizes its energy consumption during operation.

According to some embodiments, thrusters of a submersible vehiclegenerate energy-consuming dynamic buoyancy (DB) with respect to theirscalar volume. On the other hand, non-energy consuming sources, such aslift bags, produce static buoyancy (SB). Accordingly, a submersiblevehicle equipped with both lift bags (also referred herein as“opposers”) and thrusters, referred to herein collectively asopposer/thruster devices, would have, at any given time, a totalresultant buoyancy (RB) as provided by equation 3 below:

RB=SB+DB  (3).

According to some embodiments, the amount of dynamic buoyancy DBgenerated is proportional to the amount of energy E consumed (e.g.,DB∝|E|). And because both negative and positive DB consume energy E orpower P, the latter being defined as the amount of energy consumed perunit time (e.g., P=dE/dt), it would be desirable to minimize the needfor dynamic buoyancy DB to drive the power P (e.g., the energy consumedper unit time) to a minimum (e.g., DB→0, P→0). However, to maintain thetotal resultant buoyancy RB constant (or within acceptable levels)according to equation 3, the static buoyancy SB has to compensate forthe loss in dynamic buoyancy DB. In other words, minimizing DB requiresmaximizing SB to maintain a constant RB.

Challenges with Opposer/Thrust Devices

When a lift bag filled with a gas or gas mixture (e.g., air) issubmerged into water, changes in the water pressure result in an inversechange of the gas volume within the lift bag as described by Boyle'slaw, which states that the pressure of a system is inverselyproportional to its volume (e.g., P∝V⁻¹). For example, when a balloonfilled with air descends into a water column, the water pressure (e.g.,the hydrostatic pressure) surrounding the balloon increases as afunction of depth. The increasing water pressure compresses the balloonwhose volume begins to decrease (V↓) as the hydrostatic pressureincreases. At the same time, the balloon's internal pressure increases(P↑) according to Boyle's law. Conversely, when the balloon ascends, thehydrostatic pressure decreases, which allows the gas inside the balloonto expand. This also causes the balloon's volume to increase (V↑)according to Boyle's law.

Because the buoyancy acting on the balloon is proportional to its volume(which defines the amount of water being displaced), the buoyancyincreases as the balloon expands during its ascent and decreases as theballoon shrinks during its descent. Accordingly, during the balloon'sascent or descent, the buoyancy acting on the balloon changes at avariable rate as a function of depth until the fluid resistanceincreases to the point where an equilibrium condition is reached. Thismeans that a lift bag filled with a fixed amount of gas may experiencechanges in its buoyancy when its vertical position changes (e.g., itsdepth in a column of water). And because, as explained above, thebuoyancy changes at a variable rate, the buoyancy may overshoot ineither direction (e.g., become either very positive or very negative)depending on whether the lift bag ascends or descends. This effect isknown as SB overshoot. Due to this effect, the SB produced by lift bagsin opposer/thrust devices may become variable if left unchecked.Accordingly, lift bags or similar sources of SB may requiremodifications for deep-sea operation. For example, a system is requiredto inject and release gas from the lift bag during the descent andascent to account for the changes in hydrostatic pressure.

In addition, it is necessary to control second order effects or timedelay effects, such as the rate at which the SB changes when gas isinjected into or released from the lift bag of an opposer/thrust device.SB produced by lift bags stabilizes slowly as the gas settles (e.g., asthe gas reaches an equilibrium state within the volume of the lift bag),which can be substantially lower than the rate at which the DB producedby thrusters changes (e.g., dSB/dt<dDB/dt). For instance, whencompressed air is introduced into a lift bag submerged in water, it cantake up to 30 s for the gas to settle and for the buoyancy vector tostabilize. In contrast, DB provided by a thruster is practicallyinstantaneous. Therefore, when gas is injected in the lift bag of anopposer/thruster device, DB from the thruster may be used to counteractthe second order effects—e.g., until the gas settles in the lift bag.This also applies for when gas is released from the lift bag.

The combination of secondary effects with the SB overshoot makes the useof opposer/thrust devices challenging for deep-sea operations.Nevertheless, power savings can be realized when SB is used instead ofDB in scenarios where the load or weight of the deep-sea mining vehiclechanges during the mining process. For example, when the buoyancygenerated by SB devices offsets the weight of the load while DB isjudiciously used to prevent overshoot and second order effects.

Because maximizing the use of SB increases the probability of anovershoot incident or secondary effects, a balanced amount of DB may benecessary in an opposer/thrust device as discussed above. This balancedamount of DB may be optimized based on the existing conditions tominimize the consumption of energy. For example, an amount of power maybe budgeted for maneuvering the submersible vehicle when the load orweight of the vehicle changes.

Description and Operation of Opposer/Thruster Devices

According to some embodiments, a lift or a positive buoyancy source is agas-driven lift bag with or without the ability to release gas except inoverpressure conditions. Lift bags are rubber enclosures with strapsused in underwater environments. Air is a commonly used gas mixtureinjected into the bag via a compressed air housing. In some embodiments,the gas pressure inside the lift bag is greater than the surroundingunderwater pressure. If the lift bag is equipped with a release valve,by operating the release valve, gas may escape through the valve fromthe lift bag into the surrounding water due to the pressuredifferential.

Overpressure, as used herein, describes the condition where the lift bagis allowed to release air via a release valve to maintain its structuralintegrity. In the event that pressure release is not an option whenthere is lift (e.g., positive buoyancy), a negative thrust is necessaryto counteract the lift. Once the ascent from the lift begins, lift bagvolume expansion occurs due to Boyle's law until a maximum amount oflift is achieved (e.g., when drag prevents the lift from increasingfurther).

Over time, by slowly tuning SB lift and using limited amounts of thrustin the form of DB, energy consumption may be limited to small amounts ascompared to situations where thrust alone is used to compensate for loador weight increase, according to some embodiments. For example, acontrol loop system may be used to provide limited amounts of DB viathrusters while SB produced by lift bags is used to provide the majorityof the buoyancy required to offset the load or the weight increase.

According to some embodiments, FIG. 2 is a schematic diagram of anexemplary opposer/thruster device 200 configured to operate with thecombination of SB and DB produced, respectively, by a lift bag 210 and abi-directional reversible thruster 220 (thereafter “thruster 220”). Byway of example and not limitation, opposer/thruster device 200 may beused to control the buoyancy of deep-sea mining system 100 shown in FIG.1 . In some embodiments, dynamic buoyancy system 160 can include theopposer/thruster device 200. In further embodiments, a variable load 230may represent the payload hopper 150 shown in FIG. 1 . In someimplementations, thruster 220 may be integrated with UAV 130 shown inFIG. 1 or may be a separate unit from UAV 130.

In some embodiments, lift bag 210 is a rubber enclosure equipped with atleast one gas valve 230 located at its base 210B and one or morepressure release valves 240 located at one or more side surfaces 210S.However, this is not limiting, and release valves 240 may be placed inother suitable locations on the lift bag (e.g., at a top or at a bottomsurface.) According to some embodiments, gas valve 230 is a one-wayvalve. This means that gas valve 230 allows gas to be injected into liftbag 210 but prevents gas from escaping lift bag 210. One or more gascylinders 250 containing compressed gas (e.g., air or any other suitablegas mixture) provide gas to lift bag 210 via a gas valve 230. In someimplementations, lift bag 210 has an elliptical shape with its long axisalong the vertical direction z, as shown in FIG. 2 . In otherimplementations, lift bag 210 has a circular shape or any other suitableshape.

According to some embodiments, thruster 220 provides DB to mitigateovershoot incidents or secondary effects by preventing orcounterbalancing the vertical displacement of lift bag 210 while liftbag 210 is operated—e.g., when gas is injected or released from lift bag210. In some embodiments, thruster 220 may provide thrust along the xand y directions, in addition to the z direction. In some embodiments,thruster 220 may be limited to providing thrust in the verticaldirection z while additional thrusters (not shown in FIG. 2 ) mayprovide thrust in the x-y directions.

Controlling Descent and Ascent in the Opposer/Thruster Device

In some embodiments, power reduction in descent can be achieved bycontrolling the rate of descent with lift. For instance, and during thedescent, the gas delivery can be adjusted so that the gas injected intolift bag 210 reduces the rate at which the volume of lift bag 210shrinks. Gas injection in lift bag 210 via valve 210B increases the gaspressure and counterbalances the volume compression from the increasinghydrostatic pressure. Therefore, by regulating the amount of gasinjected in the lift bag, one can control the volume compression of thelift bag 210, and thus, the rate of its descent. In other words, as theopposer/thruster device 200 descents, gas injection in lift bag 210 mayincrease at a rate that counterbalances the rate at which the volume oflift bag 210 shrinks due to the increasing hydrostatic pressure so thatthe volume of lift bag 210 shrinks at a controlled rate. This wouldallow the opposer/thruster device 200 to descent at any desirable rateirrespective of the hydrostatic pressure and avoid overshoot incidents.

In some embodiments, pressure sensors can provide pressure readings forthe hydrostatic pressure and the gas inside the lift bag 210. Suitableelectronic equipment (e.g., a controller) may then calculate the rate atwhich the pressure inside the lift bag increases as a function of thehydrostatic pressure changes. Based on this information, the gasinjection may be adjusted to control the rate of descent. If a propergas delivery adjustment is made, overshoot is prevented and thrust mayonly be used to allow for recovery from secondary effects. According tosome embodiments, pressure compensated gas regulation may be used forthe gas supply of lift bag 210 in opposer/thrust device 200.

A similar concept applies to the ascent. For example, the ascent ratemay be controlled by regulating the gas release via the pressure releasevalves 240. In some embodiments, the gas supply system may beresponsible for operating pressure release valves 240. In someembodiments, the same logic that operates the gas supply system may alsooperate the pressure release valves 240. In some embodiments, adifferent system from the gas supply system may operate the pressurerelease valves 240. As the buoyancy system ascents and the volume oflift bag 210 increases, gas may be released via the release valves 240at a rate comparable to the volume increase rate to control the ascentrate. In some embodiments, DB produced by thrusters 220 may be used tomitigate the impact of secondary effects.

Controlling Neutral Buoyancy in the Opposer/Thruster Device

In an ideal scenario, the opposer/thruster device 200 keeps thesubmersible vehicle (e.g., the deep-sea mining system 100) in aneutrally buoyant state during the ore collection process. This meansthat the submersible vehicle is able to hover over the ocean floor withminimal effort and with no need to produce large amounts of DB. Tosustain neutral buoyancy, lift bag 210 can be supplied with gas atfrequent intervals (or as required) to produce sufficient lift tocounteract the variable load 230. For example, as the weight of thevariable load 230 increases, an onboard computer may calculate theamount of gas or air required to generate enough lift to offset theweight of variable load 230 based on the hydrostatic pressure of thesurrounding water. In some embodiments, thruster 220 may provide someamount of DB to prevent SB overshooting and to eliminate any secondaryeffects during the gas injection process.

According to some embodiments, onboard systems and detectors maycontinuously collect data and dynamically calculate the amount of liftrequired to offset the payload weight based on the current hydrostaticpressure conditions. Based on this information, an appropriate amount ofgas or air may be injected into lift bag 210 while thruster 220 mayintervene to make minor corrections or when there are issues detectedwith the gas supply system of opposer/thruster 200.

Additional Considerations and Alternative User Cases

According to some embodiments, multiple opposer/thruster devices may beused to control a large weight lift from a common control, gas source,and power source. Multiple points can reduce local thrust effects closeto a water body's bottom, and as such will provide less silt, reduceecological disturbances and allow identification of items forcollection. By coordinating local pressure values (e.g., using digitallogic controlling electric actuators such as solenoid valves), it ispossible to use multiple opposer/thrust devices to control a largeweight lift, the orientation and angle of the collection vehicle's load,etc.

For example, FIG. 3 is a top view of a buoyancy system 300 featuringfour opposer/thruster devices 200 attached to a variable load 310. Inthe example of FIG. 3 , each of the four opposer/thruster devices 200includes a lift bag 210 and a thruster 220. It is noted that thrusters220 are not visible from the top view of FIG. 3 . Further, buoyancysystem 300 may include additional components which are not shown forsimplicity. These additional components may include but are not limitedto gas cylinder(s), electronic equipment, mechanical equipment,pneumatic equipment, and the like. These additional components arewithin the spirit and the scope of this disclosure. By way of exampleand not limitation, the variable load 310 is depicted having arectangular shape. However, this is not limiting and the variable load310 may have any suitable shape—e.g., square, circular, oval, and thelike. According to some embodiments, buoyancy system 300 can be part ofthe dynamic buoyancy system 160 shown in FIG. 1 . In furtherembodiments, each of the four opposer/thruster devices 200 operatesunder the same principles discussed in connection to FIG. 2 . It is tobe appreciated that buoyancy system 300 may feature additional or fewerthan four opposer/thruster devices 200 attached on suitable locations ofthe variable load's top or side surfaces. For example, buoyancy system300 may include additional smaller in size opposer/thruster devices 200anchored on additional locations of the variable load 310. It is to beunderstood that the opposer/thruster devices 200 in buoyancy system 300may be operated independently form one another to permit orientation andangle adjustment of the variable load 310—e.g., when an unevendistribution of weight occurs in the variable load 310.

A single opposer/thruster device can be used for moving diver assistedor vehicle assisted large loads—e.g. in commercial diving. When theorientation (pitch and roll) of the load being raised doesn't matter, asingle opposer/thruster device may be used. Multiple thrusters wouldallow for emergency recovery, should an opposer fails.

The opposer/thruster device disclosed herein is not limited to deep-seaoperations or the deep-sea mining system 100. According to someembodiments, energy efficient opposer/thruster device 200 may be usedfor any underwater activity related to lifting large loads and/ormaintaining neutral buoyancy in underwater vehicles or objects forextended periods of time.

Terminology

The phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting.

The term “approximately”, the phrase “approximately equal to”, and othersimilar phrases, as used in the specification and the claims (e.g., “Xhas a value of approximately Y” or “X is approximately equal to Y”),should be understood to mean that one value (X) is within apredetermined range of another value (Y). The predetermined range may beplus or minus 20%, 10%, 5%, 3%, 1%, 0.1%, or less than 0.1%, unlessotherwise indicated.

The indefinite articles “a” and “an,” as used in the specification andin the claims, unless clearly indicated to the contrary, should beunderstood to mean “at least one.” The phrase “and/or,” as used in thespecification and in the claims, should be understood to mean “either orboth” of the elements so conjoined, i.e., elements that areconjunctively present in some cases and disjunctively present in othercases. Multiple elements listed with “and/or” should be construed in thesame fashion, i.e., “one or more” of the elements so conjoined. Otherelements may optionally be present other than the elements specificallyidentified by the “and/or” clause, whether related or unrelated to thoseelements specifically identified. Thus, as a non-limiting example, areference to “A and/or B”, when used in conjunction with open-endedlanguage such as “comprising” can refer, in one embodiment, to A only(optionally including elements other than B); in another embodiment, toB only (optionally including elements other than A); in yet anotherembodiment, to both A and B (optionally including other elements); etc.

As used in the specification and in the claims, “or” should beunderstood to have the same meaning as “and/or” as defined above. Forexample, when separating items in a list, “or” or “and/or” shall beinterpreted as being inclusive, i.e., the inclusion of at least one, butalso including more than one, of a number or list of elements, and,optionally, additional unlisted items. Only terms clearly indicated tothe contrary, such as “only one of or “exactly one of,” or, when used inthe claims, “consisting of,” will refer to the inclusion of exactly oneelement of a number or list of elements. In general, the term “or” asused shall only be interpreted as indicating exclusive alternatives(i.e. “one or the other but not both”) when preceded by terms ofexclusivity, such as “either,” “one of,” “only one of,” or “exactly oneof.” “Consisting essentially of,” when used in the claims, shall haveits ordinary meaning as used in the field of patent law.

As used in the specification and in the claims, the phrase “at leastone,” in reference to a list of one or more elements, should beunderstood to mean at least one element selected from any one or more ofthe elements in the list of elements, but not necessarily including atleast one of each and every element specifically listed within the listof elements and not excluding any combinations of elements in the listof elements. This definition also allows that elements may optionally bepresent other than the elements specifically identified within the listof elements to which the phrase “at least one” refers, whether relatedor unrelated to those elements specifically identified. Thus, as anon-limiting example, “at least one of A and B” (or, equivalently, “atleast one of A or B,” or, equivalently “at least one of A and/or B”) canrefer, in one embodiment, to at least one, optionally including morethan one, A, with no B present (and optionally including elements otherthan B); in another embodiment, to at least one, optionally includingmore than one, B, with no A present (and optionally including elementsother than A); in yet another embodiment, to at least one, optionallyincluding more than one, A, and at least one, optionally including morethan one, B (and optionally including other elements); etc.

The use of “including,” “comprising,” “having,” “containing,”“involving,” and variations thereof, is meant to encompass the itemslisted thereafter and additional items.

Use of ordinal terms such as “first,” “second,” “third,” etc., in theclaims to modify a claim element does not by itself connote anypriority, precedence, or order of one claim element over another or thetemporal order in which acts of a method are performed. Ordinal termsare used merely as labels to distinguish one claim element having acertain name from another element having a same name (but for use of theordinal term), to distinguish the claim elements.

Having thus described several aspects of at least one embodiment of thisinvention, it is to be appreciated that various alterations,modifications, and improvements will readily occur to those skilled inthe art. Such alterations, modifications, and improvements are intendedto be part of this disclosure, and are intended to be within the spiritand scope of the invention. Accordingly, the foregoing description anddrawings are by way of example only.

What is claimed is:
 1. An apparatus, comprising: an opposer configuredto provide static buoyancy to the apparatus when the apparatus isunderwater, the opposer comprising a gas valve and a release valve; athruster coupled to the opposer, the thruster configured to providedynamic buoyancy to the apparatus when the apparatus is underwater; avariable load; and a gas supply system comprising a gas cylinderconnected to the gas valve of the opposer, wherein the gas supply systemis configured to inject a predetermined amount of gas from the gascylinder to the opposer via the gas valve in response to a change in avertical position of the opposer caused by a mass change in the variableload.
 2. The apparatus of claim 1, wherein the gas supply system isfurther configured to operate the release valve to release gas from theopposer in response to another change in a vertical position of theopposer caused by a mass change in the variable load.
 3. The apparatusof claim 2, wherein the change is a downward change in the verticalposition of the opposer and the other change is an upward change in thevertical position of the opposer.
 4. The apparatus of claim 1, whereinthe opposer is a lift bag.
 5. The apparatus of claim 1, wherein the gasis a gas mixture.
 6. The apparatus of claim 5, wherein the gas mixtureis air.
 7. The apparatus of claim 1, wherein the thruster is configuredto provide upward or downward thrust when the gas supply system injectsgas in the opposer.
 8. The apparatus of claim 1, wherein the thruster isbi-directional reversible thruster.
 9. The apparatus of claim 1, whereingas supply system operates with pressure compensated gas regulation. 10.The apparatus of claim 1, wherein the predetermined amount of gas isbased on the mass change of the variable load and a hydrostatic pressureof water surrounding the opposer.
 11. The apparatus of claim 1, whereinthe gas valve is a one-way valve disposed at a base of the opposer andthe release valve is disposed on a side surface of the opposer.
 12. Amethod for maintaining an underwater vehicle neutrally buoyant undervariable load conditions, the method comprising: changing a mass of avariable load attached to the underwater vehicle; in response tochanging the mass of the variable load, producing lift with aninflatable lift bag attached to the underwater vehicle by injecting anamount of gas into the inflatable lift bag, wherein the amount of gasinjected is based on the mass change of the variable load and ahydrostatic pressure of water surrounding the lift bag; and whileinjecting the gas, applying an amount of thrust to oppose changes to avertical position of the underwater vehicle until the lift produced bythe amount of gas injected becomes stable.
 13. The method of claim 12,wherein injecting the mount of gas into the inflatable lift bagcomprises injecting gas from a gas cylinder attached to the underwatervehicle via a one-way valve disposed at a bottom surface of theinflatable bag.
 14. The method of claim 12, wherein applying thrustcomprises operating a bi-directional reversible thruster attached to theunderwater vehicle.
 15. The method of claim 12, wherein changing themass of the variable load comprises increasing the mass of the variableload.
 16. The method of claim 12, wherein producing lift comprisesproducing static buoyancy.
 17. The method of claim 12, wherein applyingthrust comprises producing dynamic buoyancy.
 18. The method of claim 12,wherein injecting the amount of gas into the inflatable lift bagcomprises injecting a gas mixture into the inflatable lift bag.
 19. Themethod of claim 18, wherein the gas mixture is air.
 20. The method ofclaim 12, wherein the produced lift becomes stable after about 30 s orless.